The present invention relates to radio communication networks, and more specifically, to providing high capacity radio communication networks.
As the number of subscribers to radio communication networks increases, and their usage of these networks also increases, there is a need to increase the capacity of these radio communication networks. The capacity of a radio communication network is limited by the amount of radio resources allocated to individual coverage areas, known as cells, in the network. The amount of radio resources are determined by two factors, namely, the number of channels provided by, and the amount of interference in, the radio communication network.
When the capacity of a cell in a radio communication network is limited by the number of channels the cell is referred to as channel limited. It will be recognized that the number of frequencies employed by any particular radio communication network is limited to those allocated by government bodies. The use of these limited number of frequencies to create channels is determined by the particular access technique employed by the radio communication network. One popular access technique which is employed by networks which operate in accordance with the Global System for Mobile Communications (GSM) is a combination of Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA). The FDMA/TMDA access technique allocates channels by dividing each frequency into a number of time slots. In GSM a voice channel is typically defined by one time slot per frame, a frame comprising eight time slots. A necessary condition for the use of channels in a cell is that there is equipment, e.g., transceivers, installed to enable the transmission and reception of the channels in question. Therefore, it can be seen that in a FDMA/TDMA system the number of channels allocated to a particular cell is limited by the number of frequencies allocated to the particular cell. If all channels in a particular cell have already been allocated, or if all installed transceivers are fully occupied, additional users are blocked from accessing the radio communication network from that cell.
To avoid channel limited situations, it would be desirable to allow all cells to operate on all frequencies. However, interference from proximately located cells limits the ability to assign all frequencies to each cell. For example, depending upon the amount of power employed, communications on a particular frequency in a particular cell will cause interference to communications on the particular frequency in a proximately located cell and to frequencies adjacent to the particular frequency both in the particular cell and in the proximately located cells. It will be recognized that cells can be considered to be proximately located if communications from one cell cause interference to communications in another cell. If the interference caused by communications on one frequency in a particular cell is strong enough, communications on the one frequency or on adjacent frequencies in proximately located cells may get dropped from the network. Even if the interference caused to communications on the one frequency or on adjacent frequencies in proximately located cells is not strong enough to cause these communications to be dropped from the network, the interference may be strong enough to cause an appreciable degradation in the Quality of Service (QoS) of the communications in the proximately located cells. When a cell has additional channels to allocate, but the channels themselves contain too much interference from other channels, or if the allocation of these additional channels will cause too much interference to channels which have already been allocated for communications, the inability to allocate the additional channels is referred to as an interference limited situation.
To limit interference, with the purpose of providing sufficient service quality, radio communication networks typically will assign different portions of the frequencies allocated to the radio communication network to proximately located cells. This is known as frequency reuse. FIG. 1 illustrates a ⅓ frequency reuse pattern. In FIG. 1 all frequencies allocated to the radio communication network are divided between cells 110, 120 and 130. Similarly, all frequencies allocated to the radio communication network are divided between cells 140, 150 and 160. Accordingly, cells 110, 120 and 130 are collectively referred to as frequency reuse group, herein referred to as frequency reuse group A. Similarly, cells 140, 150 and 160 are referred to as frequency reuse group, herein referred to as frequency reuse group B. To limit the amount of interference between frequency reuse groups, the particular set of frequencies assigned to a particular cell in a reuse group is selected such that it is the furthest from the particular set of frequencies in another reuse group. For example, in FIG. 1 cells 110 and 140, cells 120 and 150, and cells 130 and 160 would be assigned the same set of frequencies, respectively. However, by dividing the number of frequencies between cells in a reuse group, the number of channels in each cell is limited to less then the total number of channels which could be allocated if all frequencies were used in each cell. Another mechanism for limiting interference is to control the power of transmissions between users and the network. Accordingly, it should be recognized that transmission power can be considered as a component of the amount of radio resources which can be allocated by the network.
Conventional techniques for addressing the channel and interference limited situations focused on networks in which only one type of service is provided, for example, voice service. However, other types of services, for example, data, are being incorporated into radio communication networks. One standard for incorporating data communications in a GSM network is known as enhanced data-rates for GSM evolution (EDGE). A third generation (3G) network which incorporates EDGE with GSM is referred to as a GSM/EDGE Radio Access Network (GERAN). Data services can be defined by the particular characteristics of the type of data being conveyed, including streaming audio and video services, pure data, for example file transfers, and the like. These services all have different requirements for communication. Voice services are typically implemented in a circuit switched manner wherein an entire channel is reserved for the voice service. This is due to the requirement of voice services of low delay tolerance and low error tolerance. However, data services are typically more tolerant of delays and more tolerant of errors, and hence are implemented in a packet switched manner. The higher error tolerance of data services is due to the ability of these services to retransmit erroneously received data. The requirements for any particular service is known in the art as a QoS requirement.
One technique for achieving the differing QoS requirements for the different types of services is to designate certain frequencies for each different type of service. However, this can be a very inefficient use of radio resources. For example, if the channels allocated for data services are not fully used while the channels allocated for voice services are at capacity, the unused channels allocated for the data services result in a waste of radio resources which could be used for the voice services.
One attempt to increase capacity while still meeting the various QoS requirements in GERAN is referred to as Dynamic Frequency and Channel Assignment (DFCA). In Dynamic Frequency and Channel Assignment (DFCA), dynamic channel allocation is performed in an attempt to maintain the various QoS requirements for each service. The dynamic channel allocation is based on dynamic measurements, statistics and prediction. However, Dynamic Frequency and Channel Assignment (DFCA) results in a high degree of complexity to obtain the gain in network capacity due to the requirement that channel re-allocation must be performed frequently. In addition, Dynamic Frequency and Channel Assignment (DFCA) relies upon frequent measurements of the present radio quality which must be processed in the radio communication network. These frequent measurements must be combined with long-term statistics to make predictions of the most suitable channel for each requesting user. To avoid overloading the system, a xe2x80x9csoft admission controlxe2x80x9d technique is utilized where users are not admitted into the system if the required radio channel cannot be provided. Moreover, Dynamic Frequency and Channel Assignment (DFCA) precludes the possibility of different services with different QoS requirements from sharing the same channel, i.e., packet switched access for different QoS requirements.
Accordingly, it would be desirable to increase the capacity of a radio communication network in view of the channel and interference limitations encountered when attempting to increase the capacity. It would also be desirable to achieve this increase of capacity in radio communication networks which support a variety of services. Further, it would be desirable to increase network capacity while still maintaining the required QoS for each service. It would also be desirable to increase network capacity without increasing the complexity of network planning. In addition, it would be desirable to increase network capacity while ensuring that the techniques employed do not prevent the introduction and the utilization of future improvements.
The present invention provides methods and apparatus for providing a high capacity radio communication network. The network employs a low frequency reuse technique between cells. The reuse technique is selected such that the assignment of channels in each cell renders the network interference limited. The reuse technique employed is Fractional Load Planning (FLP) that can be extended to extreme capacities through Channel Allocation Tiering (CHAT). The radio resources in each cell are allocated using a Service Based Power Setting (SBPS) technique such that network capacity is maximized while allowing each service group to achieve its required quality of service (QoS) requirements. To limit the interference in the network, thus maintaining/controlling the required QoS level for already admitted users, a Power Based Admission Control (PBAC) technique is employed to control the admission of new users into the network.